A beach is a strip of sand along a coastal waterbody, such as the sea or a lake. It is formed by erosion of rocks and sediments that lie offshore or by wave action reworking and depositing material on the coastline. Beaches are typically characterized by fine, silty, sandy or pebbly sediments, sometimes with some gravel, shells and algae.
Generally, the beach environment is dynamic and constantly changing. Natural beaches evolve over thousands of years as a result of erosion, deposition and accretion, and are controlled by several factors including wave parameters, sediment composition and distribution, and coastal vegetation. Beaches are commonly found as sandy stretches bordering rocky or cliffy coastlines, but can also form on lakes and alongside rivers.
The sediments that comprise a beach are primarily fine to medium-grained quartz sand derived from river sediment deposited in the ocean, and reworked by the action of waves and currents. However, some beaches contain sand from other sources, such as marine debris or fragments of other types of sediments. Depending on the composition and size of these other materials, some beaches can appear darker or more reddish in color.
Beach ridges and dunes are the characteristic features of a beach landscape, and in most cases the lower part of a beach is called a terrace. The higher parts are referred to as the face and the uppermost areas are often called the back of the beach. Some beaches may be dominated by small hummocks, or foredunes, that are known as marram (saltmaram) and often covered with plants such as seagrass.
During storms, wave and surf action erodes the land around the beach, creating a wide open area of coarse sand in front of the beach. Some beaches are also characterized by the presence of a berm, which is the edge of a platform of coarser-grained sediment that is deposited by higher waves during severe storms.
Sand movement is aided by the wind, which blows the sand in loose particles across the beach surface. Some of these particles are carried back offshore by currents, while others remain behind in the form of a sand bar. Beach nourishment activities are used to add new sand to the beach to replace material that has been eroded.
Human factors can significantly alter beach environments, and these changes are reflected in the dynamics of the beach. Urban development, dams and the rerouting of rivers may reduce the amount of erodible material that can be found near bodies of water, which in turn affects beach growth and recession rates. Beaches can also be affected by nutrient pollution, marine debris and climate change impacts such as rising sea levels. Beaches can be protected from these effects through zoning laws and environmental management practices, such as beach nourishment. In addition, many beaches are managed through tourism and conservation initiatives. Beaches are an important part of the global ecosystem, and their importance has given rise to a variety of cultural and economic benefits.